1. Field of the Invention
This invention pertains to electrical stimulation leads in general, and to cardiac pacing leads in particular.
2. State of the Prior Art
Electrical stimulation of the body for medical purposes is well known in the prior art. An example of a device for this purpose is the well-known cardiac pacemaker. In the pacemaker context, as well as other body stimulation contexts, the stimulation is delivered to the desired body site by an electrode carrying lead.
Interactions between the lead and body can vitiate the desired effects of the stimulation. For example, material reactions may encourage fibrosis. In the pacemaking context, fibrosis is believed to be a major factor in the increase in chronic stimulation threshold that is usually experienced. Also, mechanical trauma may result in inflamation of the tissue to be stimulated. Such inflamation may alter the response of the tissue to the stimulation energy, both acutely and chronically.
Other interactions between the lead and body, while not directly affecting the response of the tissue to the stimulation energy, can result in the occurrence of undesirable events. In some circumstances where electrical body stimulation is indicated, the body portion to be stimulated is irritable. The placement of a lead may compound this irritability. For example, the placement of a pacemaking lead may induce a cardiac arrhythmia. The presence of the lead may also promote thrombus formation.
The interactions noted above have long been recognized and efforts made to ameliorate their consequences. For example, the lead may be configured to reduce mechanical trauma and the response of irritable tissue during lead placement. Materials may be selected for the lead body and electrodes to minimize fibrosis. However, lead configuration must take into account other factors such as the efficiency of the delivery of the stimulation energy, the ease of lead placement, maintenance of the desired electrode position and reliability of the lead over extended periods of time. An accommodation of these interests has resulted in leads whose configuration necessarily results in undesirable interactions between the lead and body.
It is known that thrombus formation may also be countered by the administration of suitable drugs. It is also known that a systemic treatment with steroids results in acute reduction in the stimulation threshold level. In particular, systemic use of glucocorticosteroids has been used to treat chronic exit block, a condition in which the stimulation threshold rises above the output level of the implanted pacemaker. However, long term systemic use of such steroids often produces undesirable side effects.